The overall goal of this proposal is to determine the role of cGMP in neuronal development using olfactory receptor neurons (ORNs) as a model. Neuronal development and regeneration are complex processes that integrate neuronal proliferation, survival, and differentiation. Our recent data indicate that cGMP has essential roles in olfactory receptor neuronal development and maintenance. We hypothesize that cGMP modulates neuronal proliferation, survival, and maturation. The specific effect that cGMP has depends upon neuronal "status" (age and priming by other factors), and the mechanism and site of cGMP production. Cyclic GMP is produced by two classes of enzymes. [1] cGMP is generated by soluble guanylyl cyclases that are activated by the gaseous messengers NO and CO. [2] cGMP is also produced by receptor guanylyl cyclases activated by calcium and extracellular ligands. Thus, we hypothesize that in the adult olfactory system, CO produced by heme oxygenase (HO) in the olfactory epithelium mediates proliferation and survival signals, while NO produced in the olfactory bulb mediates survival through synaptic integrity. In contrast, receptor guanylyl cyclases located in dendritic membranes regulate long-term responses to stimulus detection through calcium and the ligand, atrial natriuretic peptide (CNP), mediates the maturation and survival of proliferating neuronal precursors. Aim 1will combine in vivo and in vitro approaches using knockout animals and primary cultures of ORNs and biochemical and molecular approaches to test the hypothesis that CO and NO mediate paracrine proliferation/survival or target-derived survival signals for ORNs. Aim 2 will use Western blots, antibodies to signaling cascade proteins, pharmacological agents, dominant negative approaches, biochemical second messenger assays and primary cultures to test the hypothesis that odorant-induced cGMP signaling mediates long-term responses to stimulus detection through the Ras-MAPK pathway. Aim 3 will use biochemical second messenger assays, pharmacological reagents and dominant negative approaches, to test the hypothesis that atrial natriuretic peptide C (CNP) alters cGMP levels to induce maturation and survival of growth factor primed-ORN precursors.